1. Field of the Invention
This invention relates to amorphous metallic films, and more particularly to amorphous metal films containing significant amounts of nitrogen.
2. Description of the Prior Art
U.S. Pat. No. 4,002,546 entitled "Method for Producing a Magnetic Recording Medium" of Shirahata et al describes ion plating of a Co-Si, Co-Ni-Si, Co-Fe-Si, or Co-Ni-Fe-Si magnetic alloy onto a support such as a plastic, a glass or a nonmagnetic metal. The ion plating is performed in a glow discharge of an "inert gas" such as nitrogen, helium, neon, argon, krypton, xenon, radon, mixtures thereof, etc. The gases used in the examples given were helium and argon, but not nitrogen. It is stated that ion plating of the above materials provides magnetic recording media having good adhesion to the support with excellent magnetic properties. There is no mention of the formation of an alloy including any of the "inert gases" such as nitrogen or any special effect of the use of nitrogen. There is no example or data in the patent which shows that nitrogen gas was actually used. No effect upon resistivity, magnetization (4.pi.M.sub.s), effective anisotropy field (H.sub.k.sup.*) or anisotrophy energy K.sub.u, corrosion resistance, thermal stability or mechanical hardness is mentioned. Where the sputtering gas was helium in Example I, traces of O, Ar, N and C were found, but that is not relevant. Since nitrogen is normally considered to be a reactive gas, its inclusion as an inert gas may have been an inadvertent error.
U.S. Pat. No. 3,856,513 of Chen et al makes amorphous Co-Fe-B by ejecting a molten stream onto rollers or by evaporation of Ni.sub.75 P.sub.16 B.sub.6 S.sub.3 onto a copper substrate. Use of nitrogen was not mentioned.
O'Handley et al in "New Non-Magnetostrictive Metallic Glasses," IEEE Transactions on Magnetics, Vol. MAG-12, No. 6, pp. 942-944 (November 1976) describes a bulk metallic glass alloy of Co.sub.74 Fe.sub.6 B.sub.20 with a high value of 4.pi.M.sub.s of 11.8 KG and a low value of H.sub.c of 0.035 Oe which diverge from the objects and advantages of this invention.
U.S. Pat. No. 4,038,073 of O'Handley et al entitled "Near-Zero Magnetrostrictive Glassy Metal Alloys with High Saturation Induction" describes (Co.sub.x Fe.sub.1-x).sub.a F.sub.b C.sub.c compounds which were not deposited by sputtering, ion plating, evaporation or the like. No mention of N.sub.2 was made.
U.S. Pat. No. 3,965,463 of Chaudhari et al for "Apparatus Using Amorphous Magnetic Compositions," commonly assigned, describes sputtering of magnetic amorphous materials such as Gd-Fe and Gd-Co in argon in the presence of small amounts of N.sub.2 gas, about 1 volume percent, as a way to increase or decrease the magnetization, 4.pi.M.sub.s, by changing the exchange interaction between the constituents of the composition to a higher or lower magnetization, depending upon the location on the magnetization versus composition curve. It also suggests that coercivity H.sub.c can be changed by adding O.sub.2 or N.sub.2 as dopants to adjust grain size (although amorphous materials generally do not possess granularity), since coercivity is dependent on grain size. No suggestion is made that there is an advantage to adding more than 1 or 2 percent of N.sub.2 into the plasma for improving qualities such as adhesion, corrosion, mechanical hardness, and H.sub.k.sup.* or even for the purpose of increasing a parameter such as resistivity and decreasing magnetization (4.pi.M.sub.s). Furthermore, the patent does not mention any elements such as B, Si, Al, C, and P which are remote from Gd on the periodic chart and which are unlike Gd because they are nonmagnetic and possess atomic radii of about 0.91-1.43 A whereas Gd possesses an enormous atomic radius of 1.79 A. The magnetic metals Fe, Co, and Ni all have atomic radii of from 1.24 to 1.26 A, and nitrogen has an atomic radius of 0.92 A. Since the radius of nitrogen is half that of gadolinium and since it is closer in size to the radii of the elements forming the amorphous compounds of this invention, it can be seen that N.sub.2 gas is unlikely to have the same effect upon GdFe as on CoFeB because it will fit into the structure similarly to boron. The patent mentions anisotropy K.sub.u as varying with film thickness and deposition rate and film composition, but no mention is made that nitrogen content affects H.sub.k *.
Cuomo et al "Incorporation of Rare Gases in Sputtered Amorphous Metal Films," Journal of Vacuum Science and Technology 14 No. 1, pp. 152-157, 156 (1977) states as follows: "For example, the large argon concentration in tungsten sputtered in a N.sub.2 Ar mixture.sup.10 and tungsten and tantalum in argon.sub.4 is possibly due to the W and Ta being in the amorphous state. Although the authors do not state the structure of their materials, it is known that these transition metals are readily stabilized as amorphous phases.sup.16 and would therefore readily accomodate the inert gas constituent."
U.S. Pat. No. 3,427,154 of Mader points out that a criterion of an amorphous alloy is that there should be sufficient difference between the component atomic radii to inhibit transformation by diffusion or segregation. For component atoms A and B with radii r.sub.A and r.sub.B, the size factor is defined as: ##EQU1## The results are as follows:
______________________________________ Alloy R.sub.B (A) R.sub.A (A) Percentage ______________________________________ GdFe 1.79 1.26 34% GdN 1.79 0.92 62% FeN 1.26 0.92 31% FeB 1.26 0.98 25% BN 0.98 0.92 6% SiN 1.32 0.92 36% ______________________________________
Obviously Gd is far more distinct in size from Fe and N than are B and Si, so based upon the above differences one would not consider Gd and the elements B, C, P, and Si to be closely related either in terms of size or magnetic characteristics.